The research proposed here will define further how odor information from peripheral olfactory sensory neurons is encoded by odorant receptors (ORs) and also how it is organized as it progresses to the olfactory cortex (OC). A screen will be performed to identify additional ORs that recognize thiols and structurally similar odorants with highly divergent qualitative features (e.g. hexanethiol, which has a foul odor, and hexanol, which has a sweet smell). This will be accomplished with dissociated mouse olfactory sensory neurons using Ca++ imaging and single cell PCR. ORs of similar and divergent sequences recognizing the same odorant will be targeted with knockin constructs, resulting in coexpression of differentially tagged transneuronal tracers (barley lectin). Areas of the OC containing BL will be determined with immunohistochemistry in both single and double knockin animals. This will allow determination of the overlap of multiple OR inputs to the OC. In addition to helping illuminate how OR structure is related to odorant detection, these experiments will determine whether OR inputs to the OC are organized by function and/or structure of the OR.